In Pullman and Moscow both, a ‘natural-look’ trend using railroad tie retaining walls took place from the mid-1980’s to about 2000, when masonry block supplanted the trend. The advantage of the railroad ties was the number of them dropped onto the market as local rail lines got torn up and the creosoted wood was nearly given away.
As is usually the case, the contractors that first started using the ties had no idea of what a wall constructed of wood should look like. Mostly, they pretended that it was just like a concrete wall. They stacked the ties, drove spikes through them vertically and—viola’—counted it as good.

It wasn’t. The railroad ties are prone to rotating and the spikes aren’t enough to resist the motion. Add to that the ground pressure, especially when the native loess around here gets wet, and the retaining walls tend to pick up a lean pretty quickly.

There’s a way to fix the issue, though. At the time you build the wall, you include tiebacks. Tiebacks can be made with steel rods and use anchor bolts to flat plates at the outside of the wall. A more attractive solution that works equally well is to use the railroad ties themselves as the tiebacks by turning an appropriate number of them perpendicular to the wall, extending into the hillside you are retaining.

If you look at the railroad tie retaining wall in the picture, you can see a tieback in the lower middle part of the picture where the end profile of the tie is visible.

No, I can’t tell you the appropriate number of tiebacks – that is known as engineering and I’m not qualified. As an inspector, I recognize when this has been done (and hasn’t, obviously) and point it out to the client.

Now, for the other problem with using railroad ties in retaining walls, at least in Pullman and Moscow—the ties are a multi-story hotel for carpenter ants.

The creosote coating will keep them from penetrating the surface of the wood but any cut ends or sections that split will provide an entry point. Once inside, the carpenter ants will set up house. Unlike most other wood destroying organisms in the Pacific Northwest, the ants don’t eat the wood. They excavate and create shelters.

While their presence in the wall will weaken it, they’re not yet a threat to your home until they attempt to colonize it in the same manner they took over the railroad ties. As part of a home inspection in Washington State, the inspector is required to inform you of potential conditions conducive to this type of infestation. Note the difference . . . potential. Just because the condition exists, it does not automatically follow that an infestation is imminent.

It would be prudent to have a professional keep an eye on the potential for you and, if it’s a concern, provide treatment options. A pair of companies I like are Sunpest and Hayden Pest Control. {Disclaimer-Sunpest helps me with my dandelion issues.}

Railroad tie retaining walls are an attractive landscaping feature but, when buying a new home, look for the signs (or make sure your inspector looks) of good construction and be mindful of the pest issues. Otherwise, enjoy the natural beauty they bring.